The present invention relates generally to devices to deliver powder for a process, and more specifically to a new class of powder feeders which deliver a wide range of powdered materials at a substantially constant rate.
Traditional powder feeders incorporate as part of their action the movement of powder between moving surfaces. Examples include screws, gear teeth, rotating perforated disks, or other such mechanisms which move the powder from a reservoir at a substantially constant rate. Tight mechanical tolerances are required so that such devices can provide a controlled feed rate, but these same tolerances render the device susceptible to jamming as powder collects in bearings or between moving surfaces. In addition, if hard or abrasive powders are to be delivered, the rate of wear of the mechanical components of the powder feeder can be unacceptably large. Wear is not only to be avoided for the survival of the powder feeder, but also to avoid contaminating the powder being fed. Alternately, overly soft powders can agglomerate and clog these mechanisms.
Jamming in conventional powder feeders is also exacerbated by feeding powder with a range of particle sizes. If the powder size is smaller than the separation between the moving metal surfaces in the feeder, it can collect, e.g., between bearing surfaces, causing damage and contamination of the powder by galling. If the powder size is too large, individual particles can jam and/or break the apparatus.
There is a need for a powder feeder which is robust in operation, and can supply a precisely defined and controlled delivery of powder. Desirable characteristics for such a powder feeder, based on the difficulties seen in prior art feeders, would include a minimum of moving parts, a delivery mechanism suited to feedback control of delivery rate, and a mechanism which does not undergo damage when the powder flow becomes jammed. More preferably, the feeder should possess a mechanism through which the feeder can be unjammed with a minimum of interruption.